A comparison was made, based on morphologic and immunohistochemical studies of heart tissues, of the protective effects of ICRF-187 and its L-isomer ICRF-186, against the cardiac toxicity produced by the chronic administration of doxorubicin to spontaneously hypertensive rats (which have been previously shown to be excellent models for the evaluation of this type of cardiac toxicity). The results obtained showed that ICRF- 186 is slightly less cardioprotective than ICRF-187.